Typically a conveyor belt arrangement includes a conveyor belt supported on a series of conveyor idlers located along the length of the conveyor belt. Conveyor idlers are also referred to as conveyor rollers and, in this specification, a reference to a conveyor idler includes a reference to a conveyor roller. In the art it is known to drive the conveyor belt via a motor so that the conveyor belt runs on the conveyor idlers which are rotatably connected to a support frame.
The conveyor idlers typically do not include braking means and run freely in both a forward or reverse direction. This can create problems, especially with inclined conveyor belt arrangements. If the conveyor belt snaps, or the motor trips, then the conveyor belt may move in the reverse direction under the load on the conveyor belt. This will result in the load being deposited at the back of the conveyor belt arrangement which creates a safety hazard for employees, can cause damage to surrounding structures and results in production downtime.
Brake mechanisms for conveyor belts are known, but these are usually separate mechanisms which act on the conveyor belt itself and are located adjacent the conveyor belt where they are easily damaged. In addition, because these brake mechanisms are exposed they require regular maintenance. These brake mechanisms are relatively expensive. Furthermore, if the conveyor belt breaks, then these brake mechanisms, known as hold-backs, cannot prevent the conveyor belt and its load from running backwards.
U.S. Pat. No. 1,437,718 describes a cane carrier consisting of a flexible endless conveyor having two parallel spaced endless chains with slats extending between the two endless chains. Two dogs or cams are pivotally located above the slats. The dogs have teeth which permit movement of the upper flight in the upward direction, but prevent downward movement of the upper flight by digging into the slats. The cane carrier also has two sprockets which mesh with the upper and lower flights of the two endless chains. Associated with each sprocket is a ratchet and pawl which permits the sprocket to rotate in one direction only. The sprockets thus allow the upper flights to move upwardly but not downwardly, and prevent the lower flights from moving when the pawls are engaged with their sprockets.
U.S. Pat. No. 4,548,316 describes a conveyor holdback or conveyor run-back stop mechanism. The holdback is interposed between a drive motor and a gearbox. The holdback has a one-way ratchet arrangement which permits a drum around which the conveyor belt is looped to rotate in one direction only. Provided the conveyor belt does not break, the holdback will prevent the conveyor belt from running backwards.
DE 864978 also describes a holdback which is located on a fast turning drive shaft to a gearbox. This holdback also prevents the conveyor belt from running backwards.
It is desirable to have a conveyor idler which incorporates a braking mechanism which is not exposed to the elements, permits rotation of the conveyor idler in a forward direction, and retards rotation of the conveyor idler in a reverse direction thereby providing a braking effect on the conveyor belt.